2 Nutrition in Animals

Y ou have learnt in Chapter 1 that food into simpler substances is called plants can prepare their own food digestion. by the process of photosynthesis 2.1 DIFFERENT WAYS OF TAKING FOODbut animals cannot. Animals get their The mode of taking food into the bodyfood from plants, either directly by varies in different organisms. Bees andeating plants or indirectly by eating humming-birds suck the nectar ofanimals that eat plants. Some animals plants, infants of human and manyeat both plants and animals. Recall that other animals feed on motherís milk.all organisms including humans require Snakes like the python swallow thefood for growth, repair and functioning animals they prey upon. Some aquaticof the body. Animal nutrition includes animals filter tiny food particles floatingnutrient requirement, mode of intake nearby and feed upon them.of food and its utilisation in the body. You have studied in Class VI that food Activity 2.1consists of many components. Try to What is the type of food and mode ofrecall and list them below: feeding of the following animals? Write 1. ______________________ down your observations in the given 2. ______________________ Table. You may find the list of modes of feeding given below the Table helpful. 3. ______________________ Table 2.1 Various modes of feeding 4. ______________________ 5. ______________________ Name of Kind of Mode of animal food feeding 6. ______________________ Snail The components of food such as Antcarbohydrates are complex substances. EagleThese complex substances cannot be Humming-birdutilised as such. So they are broken Licedown into simpler substances. The Mosquitobreakdown of complex components of Butterfly House fly (Scraping, chewing, siphoning, capturing Complex substance Simpler substances and swallowing, sponging, sucking etc.) Amazing fact of the stomach and the small intestine, and the various glands associated with the Starfish feeds on animals covered by canal such as salivary glands, the liver hard shells of calcium carbonate. and the pancreas secrete digestive juices. After opening the shell, the starfish The digestive juices convert complex pops out its stomach through its mouth to eat the soft animal inside the shell. The stomach then goes back into the body and the food is slowly digested. Buccal cavity

Salivary gland Oesophagus

Liver

Fig. 2.1 Starfish Stomach

Gall bladder

2.2 DIGESTION IN HUMANS Pancreas

We take in food through the mouth, Smalldigest and utilise it. The unused parts intestineof the food are defecated. Have you ever Largewondered what happens to the food intestineinside the body? The food passes Rectumthrough a continuous canal (Fig. 2.2) Anuswhich begins at the buccal cavity and Fig. 2.2 Human digestive systemends at the anus. The canal can bedivided into various compartments: substances of food into simpler ones. The(1) the buccal cavity, (2) foodpipe or digestive tract and the associated glandsoesophagus, (3) stomach, (4) small together constitute the digestive system.intestine, (5) large intestine ending in Now, let us know what happens tothe rectum and (6) the anus. Is it not a the food in different parts of the digestivevery long path? These parts together tract.form the alimentary canal (digestivetract). The food components gradually The mouth and buccal cavityget digested as food travels through the Food is taken into the body through thevarious compartments. The inner walls mouth. The process of taking food into

12 SCIENCE Milk teeth and permanent teeth Do you remember about falling of your teeth some years ago? The first set of teeth grows during infancy and they fall off at the age between six to eight years. These are termed milk teeth. The second set that replaces them are the permanent teeth. The permanent teeth may last throughout life or fall off during old age or due to some dental disease.

Molar

Boojho is fascinated by the

Premolar highly coiled small intestine seen in Fig. 2.2. He wants to know its length. Would you like to make a Canine wild guess? We have given its approximate length on page 16. Just imagine how such a long Incisor structure is accommodated in a small space within our body!

the body is called ingestion. We chew

Fig. 2.3 Arrangement of teeth and differentthe food with the teeth and break it type of teethdown mechanically into small pieces.Each tooth is rooted in a separate socket which ones for piercing and tearing?in the gums (Fig. 2.3). Our teeth vary in Also find out the ones that are used forappearance and perform different chewing and grinding?functions. Accordingly they are given Record your observations in Table 2.2different names (Fig. 2.3). Table 2.2Activity 2.2 Type of teeth Number of teeth TotalWash your hands. Look into the Lower jaw Upper jawmirror and count your teeth. Use Cutting andyour index finger to feel the teeth. biting teethHow many kinds of teeth could you Piercing andfind? Take a piece of an apple or tearing teethbread and eat it. Which teeth do Chewing andyou use for biting and cutting, and grinding teeth

NUTRITION IN ANIMALS 13 Our mouth has the salivary glands of boiled rice; in test tube ëBí keep onewhich secrete saliva. Do you know the teaspoonful of boiled rice after chewingaction of saliva on food? Let us find out. it for 3 to 5 minutes. Add 3ñ4 mL ofActivity 2.3 water in both the test tubes (Fig. 2.4). Now pour 2ñ3 drops of iodine solutionTake two test tubes. Label them ëAí and in each test tube and observe. Why isëBí. In test tube ëAí put one teaspoonful there a change in colour in the test tubes? Discuss the results with your classmates and your teacher. The saliva breaks down the starch into sugars. The tongue is a fleshy muscular organ attached at the back to the floor of the buccal cavity. It is free at the front and can be moved in all directions. Do Iodine solution you know the functions of the tongue? We use our tongue for talking. Besides, Water it mixes saliva with the food during Boiled rice chewing and helps in swallowing food. We also taste food with our tongue. It Boiled and chewed rice A B has taste buds that detect different Fig. 2.4 Effect of saliva on starch tastes of food. We can find out the

Sweets and tooth decay

Normally bacteria are present in our mouth but they are not harmfulto us. However, if we do not clean our teeth and mouth after eating, (a)many harmful bacteria also begin to live and grow in it. These bacteriabreak down the sugars present from the leftover food and releaseacids (see Chapter 5 to know what an acid is). The acids graduallydamage the teeth (Fig. 2.5). This is called tooth decay. If it is not (b)treated in time, it causes severe toothache and in extreme casesresults in tooth loss. Chocolates, sweets, soft drinks and other sugarproducts are the major culprits of tooth decay. Therefore, one should clean the teeth with a brush or datun and (c)dental floss (a special strong thread which is moved between twoteeth to take out trapped food particles) at least twice a day andrinse the mouth after every meal. Also, one should not put dirtyfingers or any unwashed object in the mouth. (d)

Fig. 2.5 Gradual decay of tooth

14 SCIENCE Sometimes when you eat in a hurry, talk or laugh while eating, you may cough, get hiccups or a choking sensation. This happens when food particles enter the windpipe. The windpipe carries air from the nostrils to the lungs. It runs adjacent to the foodpipe. But inside the throat, air and food share a common passage. Then how is food prevented from entering the windpipe? During the act of swallowing a flap-like valve closes the passage of the windpipe and guides the food into the foodpipe. If, by chance, food particles enter the windpipe, we feel choked, get hiccups or cough.

5. Now write down your observations

and label Fig. 2.6. Repeat this activity with other classmates. Fig. 2.6 Regions of the The foodpipe/oesophagus tongue for different tastes The swallowed food passes into the foodpipe or oesophagus. Look at Fig. 2.2. The foodpipe runs along the neck

position of taste buds by the following

activity. Paheli wants to know howActivity 2.4 food moves in the opposite direction during vomiting.1. Prepare a separate sample each of (i) sugar solution, (ii) common salt solution, (iii) lemon juice and (iv) juice of crushed neem leaf or bitter gourd. Food2. Blindfold one of your classmates and ask her/him to take out the tongue and keep it in straight and flat position. Oesophagus3. Use a clean toothpick to put the above samples one by one on different areas of the tongue as shown in Fig. 2.6. Use a new Stomach toothpick for each sample.4. Ask the classmate which areas of the tongue could detect the sweet, salty, Fig. 2.7 Movement of the food in the oesophagus sour and bitter substances. of the alimentary canal

NUTRITION IN ANIMALS 15and the chest. Food is pushed down by food and makes the medium in themovement of the wall of the foodpipe. stomach acidic and helps the digestiveActually this movement takes place juices to act. The digestive juices breakthroughout the alimentary canal and down the proteins into simplerpushes the food downwards (Fig. 2.7). substances.At times the food is not accepted by our The small intestinestomach and is vomited out. Recall theinstances when you vomited after eating The small intestine is highly coiled andand think of the reason for it. Discuss is about 7.5 metres long. It receiveswith your parents and teacher. secretions from the liver and the pancreas. Besides, its wall also secretes juices.The stomach The liver is a reddish brown glandThe stomach is a thick-walled bag. Its situated in the upper part of theshape is like a flattened U and it is the abdomen on the right side. It is thewidest part of the alimentary canal. It largest gland in the body. It secretes bilereceives food from the food pipe at one juice that is stored in a sac called theend and opens into the small intestine gall bladder (Fig. 2.2). The bile playsat the other. an important role in the digestion of fats. The inner lining of the stomach The pancreas is a large creamsecretes mucous, hydrochloric acid and coloured gland located just below thedigestive juices. The mucous protects stomach (Fig. 2.2). The pancreatic juicethe lining of the stomach. The acid kills acts on carbohydrates, fats and proteinsmany bacteria that enter along with the and changes them into simpler forms.

The working of the stomach was discovered by a

strange accident. In 1822, a man named Alexis St. Martin was badly hit by a shot gun. The bullet had seriously damaged the chest wall and made a hole in his stomach. He was brought to an American army doctor William Beaumont. The doctor saved the patient but he could not close the hole properly and left it bandaged (Fig. 2.8). Beaumont took it as a great opportunity to see the inside of the stomach through the hole. He made some wonderful observations. Beaumont found that the stomach was churning Fig. 2.8 Alexis St. Martin’s shotgun wound food. Its wall secreted a fluid which could digest the food. He also observed that the end of the stomach opens into the intestine only after the digestion of the food inside the stomach is completed.

16 SCIENCEThe partly digested food now reaches the proteins required by the body. This islower part of the small intestine where called assimilation. In the cells, glucosethe intestinal juice completes the breaks down with the help of oxygendigestion of all components of the food. into carbon dioxide and water, andThe carbohydrates get broken into energy is released. The food thatsimple sugars such as glucose, fats into remains undigested and unabsorbedfatty acids and glycerol, and proteins enters into the large intestine.into amino acids. Large intestineAbsorption in the small The large intestine is wider and shorterintestine than small intestine. It is about 1.5 metreThe digested food can now pass into the in length. Its function is to absorb waterblood vessels in the wall of the intestine. and some salts from the undigested foodThis process is called absorption. The material. The remaining waste passesinner walls of the small intestine have into the rectum and remains there asthousands of finger-like outgrowths. semi-solid faeces. The faecal matter isThese are called villi (singular villus). removed through the anus fromCan you guess what the role of villi could time-to-time. This is called egestion.be in the intestine? The villi increasethe surface area for absorption of the 2.3 DIGESTION IN GRASS-EATINGdigested food. Each villus has a network ANIMALSof thin and small blood vessels close to Have you observed cows, buffaloesits surface. The surface of the villi and other grass-eating animalsabsorbs the digested food materials. The chewing continuously even whenabsorbed substances are transported they are not eating? Actually, theyvia the blood vessels to different organs quickly swallow the grass and storeof the body where they are used to build it in a part of the stomach calledcomplex substances such as the rumen (Fig. 2.9). Here the food gets

Diarrhoea Sometime you may have experienced the need to pass watery stool frequently. This condition is known as diarrhoea. It may be caused by an infection, food poisoning or indigestion. It is very common in India, particularly among children. Under severe conditions it can be fatal. This is because of the excessive loss of water and salts from the body. Diarrhoea should not be neglected. Even before a doctor is consulted the patient should be given plenty of boiled and cooled water with a pinch of salt and sugar dissolved in it. This is called Oral Rehydration Solution (ORS).

NUTRITION IN ANIMALS 17 Ruminants have a large sac-like structure called rumen between the Paheli wants to know why oesophagus and the small intestine these animals cannot chew (Fig. 2.9). The cellulose of the food is food properly at the time they digested here by the action of certain take it in? bacteria which are not present in humans. So far you have learnt about animals which possess the digestive system. But there are many small organisms which Boojho wants to know why do not have a mouth and a digestive we cannot digest cellulose system. Then, how do they acquire and like the cattle do. digest food? In the section below you will learn another interesting way of food intake.partially digested and is called cud. 2.4 FEEDING AND DIGESTION INBut later the cud returns to the mouth AMOEBAin small lumps and the animal chews Amoeba is a microscopic single-celledit. This process is called rumination and organism found in pond water. Amoebathese animals are called ruminants. has a cell membrane, a rounded, dense The grass is rich in cellulose, a type nucleus and many small bubble-likeof carbohydrate. Many animals, vacuoles (Fig. 2.10) in its cytoplasm.including humans, cannot digest Amoeba constantly changes its shapecellulose. and position. It pushes out one, or Small Intestine Oesophagus more finger -like projections, called Rumen pseudopodia or false feet for movement and capture of food. Amoeba feeds on some microscopic organisms. When it senses food, it

18 SCIENCEpushes out pseudopodia around the growth, maintenance and multiplication.food particle and engulfs it. The food The undigested residue of the food isbecomes trapped in a food vacuole expelled outside by the vacuole.[Fig. 2.10). The basic process of digestion of Digestive juices are secreted into the food and release of energy is the samefood vacuole. They act on the food and in all animals. In a later chapter youbreak it down into simpler substances. will learn about the transport of foodGradually the digested food is absorbed. absorbed by the intestine to the variousThe absorbed substances are used for parts of the body.

What you have learnt

Animal nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body. The human digestive system consists of the alimentary canal and secretory glands. It consists of the (i) buccal cavity, (ii) oesophagus, (iii) stomach, (iv) small intestine, (v) large intestine ending in rectum and (vi) anus. The main digestive glands which secrete digestive juices are (i) the salivary glands, (ii) the liver and (iii) the pancreas. The stomach wall and the wall of the small intestine also secrete digestive juices. The modes of feeding vary in different organisms. Nutrition is a complex process involving: (i) ingestion, (ii) digestion, (iii) absorption, (iv) assimilation and (v) egestion.

NUTRITION IN ANIMALS 19 Digestion of carbohydrates, like starch, begins in the buccal cavity. The digestion of protein starts in the stomach. The bile secreted from the liver, the pancreatic juice from the pancreas and the digestive juice from the intestinal wall complete the digestion of all components of food in the small intestine. The digested food is absorbed in the blood vessels from the small intestine. The absorbed substances are transported to different parts of the body. Water and some salts are absorbed from the undigested food in the large intestine. The undigested and unabsorbed residues are expelled out of the body as faeces through the anus. The grazing animals like cows, buffaloes and deer are known as ruminants. They quickly ingest, swallow their leafy food and store it in the rumen. Later, the food returns to the mouth and the animal chews it peacefully. Amoeba ingests its food with the help of its false feet or pseudopodia. The food is digested in the food vacuole.

Exercises

1. Fill in the blanks:

(a) The main steps of nutrition in humans are __________, __________, __________, _________ and __________. (b) The largest gland in the human body is __________. (c) The stomach releases hydrochloric acid and ___________ juices which act on food. (d) The inner wall of the small intestine has many finger-like outgrowths called _________. (e) Amoeba digests its food in the ____________ . 2. Mark ëTí if the statement is true and ëFí if it is false: (a) Digestion of starch starts in the stomach. (T/F) (b) The tongue helps in mixing food with saliva. (T/F) (c) The gall bladder temporarily stores bile. (T/F) (d) The ruminants bring back swallowed grass into their mouth and chew it for some time. (T/F) 3. Tick () mark the correct answer in each of the following: (a) Fat is completely digested in the (i) stomach (ii) mouth (iii) small intestine (iv) large intestine

20 SCIENCE (b) Water from the undigested food is absorbed mainly in the (i) stomach (ii) foodpipe (iii) small intestine (iv) large intestine 4. Match the items of Column I with those given in Column II: Column I Column II

Food components Product(s) of digestion

Carbohydrates Fatty acids and glycerol Proteins Sugar Fats Amino acids 5. What are villi? What is their location and function? 6. Where is the bile produced? Which component of the food does it help to digest? 7. Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also. 8. Why do we get instant energy from glucose? 9. Which part of the digestive canal is involved in: (i) absorption of food ________________. (ii) chewing of food ________________. (iii) killing of bacteria ________________. (iv) complete digestion of food ________________. (v) formation of faeces ________________. 10. Write one similarity and one difference between the nutrition in amoeba and human beings. 11. Match the items of Column I with suitable items in Column II

Column I Column II

(a) Salivary gland (i) Bile juice secretion

(b) Stomach (ii) Storage of undigested food

(c) Liver (iii) Saliva secretion

(d) Rectum (iv) Acid release

(e) Small intestine (v) Digestion is completed

(f ) Large intestine (vi) Absorption of water

(vii) Release of faeces

NUTRITION IN ANIMALS 21 12. Label Fig. 2.11 of the digestive system.

Fig. 2.11 A part of human digestive system

13. Can we survive only on raw, leafy vegetables/grass? Discuss.

Extended Learning — Activities and Project

1. Visit a doctor and find out: (i) Under what conditions does a patient need to be on a drip of glucose? (ii) Till when does a patient need to be given glucose? (iii) How does glucose help the patient recover? Write the answers in your notebook. 2. Find out what vitamins are and get the following information. (i) Why are vitamins necessary in the diet? (ii) Which fruits or vegetables should be eaten regularly to get vitamins? Write a one-page note on the information collected by you. You may take help of a doctor, a dietician, your teacher or any other person, or from any other source.

22 SCIENCE 3. Collect data from your friends, neighbours and classmates to know more about ìmilk teethî. Tabulate your data. One way of doing it is given below: S. No. Age at which Age at which No. of teeth No. of teeth first tooth fell last tooth fell lost replaced 1. 2. 3. 4. 5.

Find out from at least twenty children and find the average age at which children lose the milk teeth. You may take help of your friends.

Did you know?

Fats in goatís milk are much simpler than those in cowís milk. Therefore, the goatís milk is much easier to digest than the cowís milk.